1. Field of the Invention
The present invention relates generally to binder compositions.
2. Background Information
Polyphenylene polymethylene polyisocyanate (PMDI) has been extensively used as a binder in the commercial production of cellulosic based wood composites such as lignocellulosic composite panels. One of the advantages of using PMDI in the production of such composites is that the binder imparts various physical and mechanical properties to the product in addition to enhancing the processability (e.g., production times) of such composites. For example, improved processability includes process efficiencies such as shorter pressing cycle times which results in increased production of the end product.
In some embodiments, lignocellulosic composite panels are manufactured by introducing a binder, such as pMDI, into a rotary blender that contains lignocellulosic particles. After the binder and the particles have been mixed, the mixture can be introduced into a mold or a press where it is subjected to heat and pressure (e.g., pressing process) thereby forming the composite panel. One drawback with the pressing process, however, is that long pressing times are typically required to cure the binder. While the composite panel manufacturer can increase the cure rate of the binder by using urethane catalysts known in the art, one drawback with the use of such catalysts is that additional binder must be used to compensate for the binder that is inactivated, which is due to pre-cure of the binder, prior to subjecting the mixture of binder and particles to a pressing process. In these instances, the manufacture typically suffers additional costs associated with using more binder than what was anticipated.
Pre-cure of the binder is also a concern in cases where a mixture of lignocellulosic particles and binder are not subjected to a pressing process in a timely manner. Typically, the cause of such delays is due to mechanical problems in the processing equipment. Therefore, there is a need to have a binder system that can offer an induction period in which binder pre-cure is minimal prior to application of heat and pressure (i.e., latency or latent cure) while also exhibiting the ability to undergo rapid cure after the application of heat and pressure (i.e., fast cure or rapid cure) thereby allowing for the efficient production of a composite product.